Coating articles with metal



July 29, 1958 A. w. scHRor-:DER 2,845,365

coATTNG ARTICLES WITH METAL l Filed July 1e, 195e .AVI

wie @i United States PatentO i COATING ARTICLES WITH METAL Albert W. Schroeder, La Grange, Ill., assignor to Chicago Metallizing Company, Inc., Chicago, lll., a corporation of Illinois Y Application July 16,1956, Serial No. 597,979

4 Claims. (Cl. 117-65) This invention relates to an improvement in the art of coating objects with metal, i. e., metallizing, and the invention will be hereinafter explained in connection with the internal aluminum coating of ferrous metal pipes of substantial length, but it should be understood that the invention maybe applied to the coating of other articles and pipers, whether internally or externally or both.

Ferrous metal pipe used in various phases of the petroleum industry and for various chemical processes have heretofore been internally coated with aluminum to protect the pipe against deterioration by the chemical action thereon of hydrogen sulphideand other sulphides or other chemicals which corrodethe pipes. One of the problems encountered in the coating of ferrous metal pipe is that of obtaining a non-porous coating of aluminum effectively fused to the ferrous metal pipe. In a known process, aluminum is sprayed on the suitably cleaned internal surface of the pipe, thereby forming an aluminum coating which is porous. With this internal coating the pipe is then subjected to a heat treatment to fuse the coating into a non-porous skin and to cause the coating to become securely bonded to the pipe. In the prior practical process, this heat treatment has required, as a preliminary thereto, coating of the aluminum coating with a suitable sealer such as a hydrolyzed solution of ethyl silicate or -other material which serves to prevent oxidation of the .ferrous metal during the heat treatment. `The sealers #during the heat treatment are vaporized and create probllems of Venting or other disposal of the vapor or gas 'resulting from the Sealers, and in other respects are not wholly adequate for their purpose.

The main object of the present invention is to vprovide an improved metallizing process of the character indicated; and to provide such a process in which the oxidation problem is more effectively solved and oxidation incident to heating of the coated pipe is prevented in a simplified manner. Other objects of the invention are to provide a process whereby very long pipe lengths may be electively metallized; to provide a process which will produce an effectively bonded and impervious or non-porous metal coating ona ferrous metal surface; and other objects and advantages of the invention will be understood by reference to the following specification and accompanying drawing wherein there is described and illustrated a metallizing process embodying a selected form of the invention.

In the drawing:

Fig. 1 is a schematic representation of apparatus employed for carrying out the improved process; and,

Fig. 2 is a diagrammatic representation of the steps of the improved process.

In Fig. l, a length of pipe 1 is represented as being rotatably supported by a series of pairs of roller supports 2. The pipe 1 may be of `any desired length, including lengths of the order of forty or fifty feet or more if desired. The roller supports 2 are xedly mounted on an I-beam base frame or other suitably constructed base frame 3. A spray gun 4 is mounted on said base 3 for Patented July 29, 1958 ICC 2 longitudinal movement relative to the pipe 1. Said spray gun comprises a carriage or car 5 which is movably mounted on suitable Vrails 6 carried by said base, an elongated tube `structure 7 which is secured at one end to said carriage 5 so as to be movable therewith longitudinallyof the pipe 1, and a nozzle 8 at the freey end of said tube or pipe structure 7. The pipe structure-7 may be supported jnear its nozzle end by a suitable roller support 9 which may bestationarybut suitably adjustable to coaxially align the nozzle Sand pipe structure 7 with thepipe 1. The carriage 5 l,is also `preferably provided with adjustmentsfor facilitating said coaxial alignment of the pipe structure 7 with the pipe 1 which is to be coated. As an alternative, thesupports for the pipe 1 may be ladjustably mounted for aligning the supported pipe 1 with the longitudinally movable spray strucshould be carefullyperfor'med so as to insure a thoroughly ture, or appropriate adjustments may beprovided in respect of both the spray gun support and the pipe support.

In this instance, the spray gun structureV is longitudinally movable through the rotated but'longitudinally stationary pipe 1 but this arrangement may be reversed if desired to cause the rotated pipel to be` moved longitudinally over a stationary spray gun or both thespray gun and the pipe may be moved4 relative to each other to attain the desired telescopic movement between these parts. The spray gun structure 7 may be reciprocated byl means of a conveyor chain or belt 10 which is guided around suitable sprockets or pulleys 11 and 12 mounted on the base structure 3 and driven in any suitable manner (not shown). The chainor belt 10 is, of course, suitably connected to the carriage 5 and the driving mechanism should be readily reversible to permit the required in and out movement of thespray mechanism relative to the pipe 1. The spray mechanism 4 acts on aluminum wire 13 which is suitably fed throughV the pipe :structure 7 to the nozzle Siwhere the wire is'melted and sprayed out, preferably in the form of a hollow cone, so as to deposit the sprayed metal uniformly around the entire inside surface of the pipe 1. Metal spraying guns such as described are known" in the art.

To effect spraying ofthe inside of the pipe 1, the spray structure 4 is advanced to pass thenozzle 8 through the pipe 1 and to locate the nozzle'adjacent the remote end 14 of the pipe. The nozzle 8 is i then 'tired and the aluminum wire 13 fed to produce the requiredspray of metal and the spray structure is then retracted so that during the retraction and withdrawal of the nozzle 8 from the pipe 1 the inside surface of the pipe will receivev the desired coating of aluminum. ,During this spraying operation, the pipe 1 is preferably rotated, this being readily accomplished by'suitably driving one or more of the supporting trolls 2 by known means not herein shown.

Before the aluminum coating is sprayed on the inside 'of the pipe, the inside thereof is thoroughly cleaned and vcleaning operation employing sand, steel grain,or other abrasive material;y When sand is used, a verysatisfactory grain size is Gl6 to G-25. `This blast cleaning operation serves to removera protective coating of dope-which is usually applied to the pipe at the pipe-makingmill to prevent corrosion While the pipe iscin transportation and storage, and also to remove any other foreign matter which may have found its way into the pipe. Sand or like blasting of the inside ofthe pipe also roughens the inside surface of the pipe to a desirable degree for facilitating adherence and bonding of the sprayed aluminum coating to 4suchlsurface. `This cleaning operation clean surface on the inside of the pipe and a substantially uniformly roughened internal surface. This cleaning step is represented in the diagram Fig. 2 by the box 15.

The next step is to spray the aluminum coating on the inside surface of the pipe in the manner above described. The thickness of the aluminum coating may be varied as desired, a minimum thickness for effective protection of the pipe in most cases being about three mills (.003"). A coating having a thickness of about fifteen mills (.0l5) is preferred for most purposes but it may, as already indicated, be made to suit any preference in this respect. This spray coating step is represented by the box 16 in Fig. 2.

The next step in the process is to seal the ends of the pipe 1 and lill it with an inert gas-such as nitrogen for example-all air and oxygen being thereby displaced from within the pipe. Other inert gases which may be used comprise argon, krypton, and others. This displacement of air and lling of the pipe with an inert gas may be effected in many ways, for example by providing end closures for the pipe, each of which is provided with a suitable valved opening to permit the delivery of the inert gas into one end of the pipe and the escape from the other end of air. After the inside of the pipe is free of air and filled with the selected inert gas, the valves in the end closures are shut off so as to retain the inert gas in the pipe. This step of protecting the pipe with inert gas is represented by the box 17 in Fig. 2.

The closed pipe with its fill of inert gas is then subjected to heat treatment whereby the aluminum coating is fused into an impervious skin or lining and also effectively bonded to the cleaned and roughened wall of the pipe. It appears that the aluminum lining is, in effect, fused to the ferrous metal pipe even though the heating temperature is normally somewhat below the melting temperature of the pipe metal. The depth of such aluminum-ferrous metal fusion is shallow enough that there remains an unadulterated inside coating of aluminum which effectively shields the ferrous metal of the pipe from attack by corrosive chemicals. Whether or not there is a true fusion of aluminum with the metal of the pipe there appears to be such an intermingling of a shallow depth of aluminum and pipe metal (about three mills when the sprayed-on aluminum layer is of fifteen mills thick) that the fused aluminum coating is practically inseparably bonded to the pipe. This depth of the bonding layer will, of course, vary somewhat with the depth of the sprayed-on coating of aluminum, the composition of the pipe metal, the temperature at which the pipe with the sprayed-on aluminum coating is treated, the time of treatment, and perhaps other factors.

The temperature of treatment is generally within the range of about 1250" F. to l450 F. and the time of treatment is inversely proportional to the temperature.

A preferred range of temperatures is from 1275 F. to l350 F. with the time of treatment varying from 45 minutes to 20 minutes according to the temperature employed. Treatment at l300 F. for one-half hour is presently considered most satisfactory in respect of the results obtained, the problems involved in the production of said temperature, and the time of treatment. At 1250 F., treatment of a fifteen mill coating for one hour produces very satisfactory results and at 1450 F., treatment of a fifteen mill coating for from ten to fifteen minutes produces very satisfactory results. From the foregoing it will be seen that the treatment temperature and time factors may be varied through a considerable range while obtaining satisfactory results.

This heat treatment step may be effected in a suitable furnace by means of an electrical induction heating coil. lt may be carried on in respect of the entire pipe length although it may be carried on progressively from one end of the pipe to the other by effecting relative movement between the `pipe and the heating means which, in that case, would act on a limited length of the pipe. The furnace may be heated in any suitable manner whereby the required temperatures may be maintained for the required length of time. After the treatment is completed, the inert gas still in the pipe is permitted to escape and the pipe is cooled in the atmosphere. This treatment leaves the pipe with an impervious, internal lining or skin of pure aluminum securely bonded to the interior of the pipe to protect the same from corrosion as already explained.

In the described process, the replacement of air with an inert gas serves to prevent oxidation of the ferrous metal of the pipe during the heating thereof to convert the porous sprayed-on aluminum coating into an impervious lining. The use of an inert gas instead of applying a sealer to the aluminum coating is a much simpler operation than that of applying a sealer coating by spraying, brushing or otherwise, especially in respect of long pipe sections such as above referred to. In addition to the indicated simplification, a further advantage is obtained by the use of an inert gas instead of a sealing coating in that the problem of disposal of the fumes which result from heating the usual sealers is eliminated. The improved method furthermore eliminates the handling of the sealing liquid and the mess which usually attends the use of such liquids in pipe coating processes.

The described use of inert gas for preventing oxidation of the ferrous metal in the object to be coated is also somewhat more effective than the use of sprayed-on sealer coatings for prevention of oxidation, probably for the reason that the inert gas method completely removes atmospheric oxidation from Contact with the object so that there is, for practical purposes, no oxidizing agent in contact with the surface being treated. In the conventional process in which a sealing liquid is employed to prevent oxidation, air remains in contact with the sealed surface and frequently leaks through the protective sealer to cause at least slight oxidation of the metal of the surface being treated, thereby causing detrimental iiaws in the fused aluminum coating formed incident to the heating step. Also, the use of an inert gas avoids the difficult problem of applying an adequate, unbroken coat of sealer to the interior of a length of pipe, especially in respect of a long length of pipe such as forty or fty feet.

It will be apparent to those skilled in the art that the foregoing described processes of coating a ferrous metal pipe with aluminum to form a securely bonded, impervious lining or skin may be applied to articles other than pipe. For example, ferrous metal plates, sheets, castings, bowls and other articles too numerous to mention may be coated by the described procedure, except that the coating of such other articles will be somewhat simplified by the elimination of the special problems of moving a spray gun through a long pipe section. Various adaptations of the described method and modifications thereof may be made while retaining the principles of the described invention.

I claim:

1. The method of coating a ferrous metal object with aluminum, which method comprises the steps of cleaning and roughening the surface to be coated, spraying a coating of liquified aluminum on said surface, displacing air from contact with said coated surface and covering the same with an oxygen-free inert gas, and while maintaining said covering of inert gas, heating the object to a temperature above the melting point of aluminum to fuse said aluminum coating into a substantially impervious layer securely bonded to the surface of said object.

2. The method of coating a ferrous metal object with aluminum, which method comprises the steps of blasting the object surface which is to be coated with abrasive material to clean and roughen said surface, spraying a coating of molten aluminum on said cleaned and roughened sur- ,5 face, displacing air from said surface which is coated as aforesaid and covering the same with oxygen-free inert gas at about atmospheric pressure, and heating the object so coated and covered to a temperature within the ran-ge of about 1250 F. to 1450 F. for a period of time Within the range of about ten minutes to one hour to convert said sprayed aluminum coating into an impervious, fused aluminum skin securely bonded to said object.

3. The method of internally coating a ferrous metal pipe with aluminum, which method comprises the steps of blasting the inside surface of the pipe with abrasive material to clean and roughen said surface, spray-coating said cleaned and roughened surface with molten aluminum to form an aluminum coating having a thickness of at least three mills, displacing air from the inside of the pipe and filling the same with oxygen-free inert gas at about atmospheric pressure, and heating the pipe containing said inert gas to a temperature withinrthe range of about 1250 F. to 1450 F. for a time period within the range of about ten minutes to one hour to cause said sprayed aluminum coating to fuse into an impervious skin securely bonded to said pipe surface.

4. The method of coating the inside of a ferrous metal pipe with aluminum, which method comprises the steps of blasting the inside surface of the pipe with abrasive material to clean and roughen said surface, spray coating said cleaned and roughened surface with molten aluminimum to for/m an aluminum coating having a 7thickness References Cited in the le of this patent UNITED STATES PATENTS 1,121,308 Thomas Dec. 15, 1914 1,914,774 Govers June 20, 1933 2,414,923 Batcheller Jan. 28, 1947 2,423,857 Talmage July 15, 1947 2,490,543 Robertson et al. Dec. 6, 1949 2,683,436 Marantz July 13, 1954 

1. THE METHOD OF COATING A FERROUS METAL OBJECT WITH ALUMINUM, WHICH METHOD COMPRISES THE STEPS OF CLEANING AND ROUGHENING THE SURFACE TO BE COATED, SPRAYING A COATING OF LIQUIFIED ALUMINUM ON SAID SURFACE, DISPLACING AIR FROM CONTACT WITH SAID COATED SURFACE AND COVERING THE SAME WITH AN OXYGEN-FREE INERT GAS, AND WHILE MAINTAINING SAID COVERING OF INERT GAS, HEATING THE OBJECT. TO A TEMPERATURE ABOVE THE MELTING POINT OF ALUMINUM TO FUSE SAID ALUMINUM COATING INTO A SUBSTANTIALLY IMPERVIOUS LAYER SECURELY BONDED TO THE SURFACE OF SAID OBJECT. 